1. Field of the Invention
The invention relates to an instrument having a liquid crystal display arranged behind a glass cover, in which the hollow space between the front glass and the liquid crystal display is filled with an immersion medium.
2. Description of the Prior Art
In instruments having a liquid crystal display, for example measuring instruments, calculators and watches, the liquid crystal display element is located in a casing, the front side of which consists of a glass or plastic glass or of a industrial glass or sapphire glass. The liquid crystal display is located a few tenths of a millimeter behind this. Even when the liquid crystal display is in contact with the glass cover, minimal hollow spaces exist between the liquid crystal display and the glass cover. However even when the transparency of the glass is good, reflections and refractions arise at the top surfaces of the glass cover and at the surface of the display element and, in the case of unfavorable lighting conditions, for example in poor lighting or in the case of light incident vertically on the glass cover and dark surroundings, it is difficult to read the information displayed and to reduce the contrast of the display.
It is known from German Offenlegungsschrift 2,538,809 to improve the readability of the information shown by liquid crystal displays by filling the hollow space between the glass cover, and the liquid crystal display with an immersion medium. The immersion medium used for this is silicone oil or silicone rubber. This solution has proved advantageous with regard to the readability. Silicone oil is used when the distances between the glass cover and the liquid crystal display are very small and silicone rubber is used when these distances are less than 0.4 mm.
Silicone oil is of such low viscosity that such an immersion medium can be drawn out of the hollow spaces as a result of capillary interaction with the gaps and crevices in the module and between the module and the casing. This capillary interaction can produce formation of air bubbles in the watch display, which causes considerable difficulty in reading the information displayed. Complete sealing of the hollow space between the glass cover and the liquid crystal display would preclude the capillary interaction of the silicone oil, but displacement of air from the hollow space during assembly of the instrument is then no longer possible.